1. Field of the Invention
The invention refers to a shield advancing machine comprising cutting tools rotatably supported on cantilever arms being rotatable around an axis approximately extending in advancing direction and being swivellable in transverse direction to this axis.
2. Description of the Prior Art
A shield advancing machine of the initially mentioned type can, for example, be taken from U.S. Pat. No. 4 248 481. In this known construction several cutting arms are supported on the outer side of a central tube, noting that each of these cutting arms is provided with a separate drive means. In this case, there is provided at the outer side of the central tube a toothed wheel extending in circumferential direction and being in meshing engagement with pinions of the drive motors arranged on sliding carriages guided in circumferential direction and having swivellably linked thereto the cutting arms. In this manner, the central tube represents a carrier for the cutting arms performing their working movements. On account of the tubular shape, the swivelling angle of cutting arms being arranged on the outer side of the tube is, however, limited in direction to the center and the cutting forces must, as a whole, be resisted by the guide means of the shifting path of the sliding carriages having swivellably supported thereon the cutting arms. In this known construction, there is arranged within the hollow central tube a further cutting arm, which can be swivelled and which is additionally rotatably supported.